Method for manufacturing silicon carbide semiconductor device

ABSTRACT

Provided is a method for manufacturing a silicon carbide semiconductor device capable of preventing an increase in a cost of manufacturing one chip while favorably maintaining forward characteristics of the semiconductor device including (a) inspecting the characteristics of the forward conduction of body diodes as element structures; (b) classifying the body diode and the body diode as either a first group suitable for forward conduction or a second group unsuitable for forward conduction on the basis of an inspection result; and (c) manufacturing a silicon carbide semiconductor MOSFET that requires forward conduction using the body diode classified into the first group or manufacturing a silicon carbide semiconductor MOSFET that does not need forward conduction using the body diode classified into the second group.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a siliconcarbide semiconductor device having a structure that performs a bipolaroperation in a silicon carbide semiconductor element.

BACKGROUND ART

Silicon carbide semiconductor devices having structures that include pnjunctions and perform bipolar operations have conventionally hadproblems that in a case where currents flow in a forward direction ofthe pn junctions, recombination currents of the pn junctions expand alamination defect due to a crystal defect, resulting in an increase in aresistance of the forward characteristics. The crystal defect causingthe lamination defect is formed in steps of manufacturing semiconductorsubstrates and epitaxial layers on the semiconductor substrates.

For example, Japanese Patent Application Laid-Open No. 2010-135573proposes a technique for observing location coordinates of a crystaldefect in a substrate by an optical microscope or the like in advance toprevent the crystal defect included in an epitaxial layer of thesemiconductor device and for forming an element region in a positionthat avoids the location coordinates of the crystal defect.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2010-135573

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, the proposed conventional technique removes, as a defectiveproduct, a semiconductor chip of the portion having the crystal defectformed therein. Thus, yields are decreased and a cost of manufacturingone chip is increased by the amount of removed chips.

The present invention has been made in view of the above-mentionedproblems, and an object thereof is to provide a method for manufacturinga silicon carbide semiconductor device capable of preventing theincrease in the cost of manufacturing the one chip while favorablymaintaining forward characteristics of the semiconductor device.

Means for Solving the Problems

A method for manufacturing a silicon carbide semiconductor device thathas an element structure including an epitaxial layer of a firstconductivity type formed on a silicon carbide semiconductor substrate ofa first conductivity type and an impurity layer of a second conductivitytype formed in contact with the epitaxial layer, the method according toone aspect of the present invention including the steps of: (a)inspecting characteristics of a forward conduction between the epitaxiallayer and the impurity layer in the element structure; (b) classifyingthe element structure as a first group suitable for the forwardconduction or a second group unsuitable for the forward conduction onthe basis of an inspection result of the step (a); and (c) manufacturingthe silicon carbide semiconductor device that needs the forwardconduction in the element structure using the element structure of thefirst group or manufacturing the silicon carbide semiconductor devicethat does not need the forward conduction in the element structure usingthe element structure of the second group.

A method for manufacturing a silicon carbide semiconductor device thathas an element structure including an epitaxial layer of a firstconductivity type formed on a silicon carbide semiconductor substrate ofa first conductivity type and an impurity layer of a second conductivitytype formed in contact with the epitaxial layer, the method according toanother aspect of the present invention including the steps of: (a)inspecting characteristics of a forward conduction between the epitaxiallayer and the impurity layer in the element structure; (b) manufacturingthe silicon carbide semiconductor device using the element structure;and (c) classifying the silicon carbide semiconductor device that hasbeen manufactured as the silicon carbide semiconductor device having theelement structure of a first group suitable for the forward conductionor the silicon carbide semiconductor device having the element structureof a second group unsuitable for the forward conduction on the basis ofan inspection result of the step (a).

Effects of the Invention

According to the above-mentioned aspects of the present invention, theelement structure (or the silicon carbide semiconductor device) isclassified as the element structure of the first group (or the siliconcarbide semiconductor device having the element structure of the firstgroup) or the element structure of the second group (or the siliconcarbide semiconductor device having the element structure of the secondgroup), and the silicon carbide semiconductor device is manufacturedaccording to each use. Thus, the silicon carbide semiconductor devicecan be manufactured by effectively using the element structureunsuitable for the forward conduction, so that the increase in the costof manufacturing the one chip can be prevented while the forwardcharacteristics of the silicon carbide semiconductor device for each useare favorably maintained.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart illustrating an outline of a method formanufacturing a silicon carbide semiconductor device according to anembodiment of the present invention;

FIGS. 2 and 3 are diagrams illustrating examples of silicon carbidesemiconductor MOSFETs that are manufactured;

FIG. 4 is a flow chart illustrating an outline of a method formanufacturing a silicon carbide semiconductor device according to anembodiment of the present invention; and

FIG. 5 is a diagram illustrating an example of a silicon carbidesemiconductor MOSFET that is manufactured.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings.

First Embodiment Manufacturing Method

FIG. 1 is a flow chart illustrating an outline of a method formanufacturing a silicon carbide semiconductor device according to anembodiment of the present invention. In this embodiment, a siliconcarbide semiconductor Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET) is assumed as an example of the semiconductor device.

First, a substrate manufacturing step of manufacturing a semiconductorsubstrate of a first conductivity type is performed (step S1).Specifically, a silicon carbide substrate is manufactured by an improvedsublimation approach (improved Rayleigh approach). In addition, acommercial silicon carbide substrate that has been already manufacturedmay be bought and used in the following steps.

At this time, to suppress an expansion of a lamination defect occurringin a case where a current flows in a forward direction of a pn junction(forward conduction), the silicon carbide substrate having a low densityof crystal defects including basal plane dislocation is preferablymanufactured.

Next, an epitaxial layer manufacturing step of forming an epitaxiallayer of a first conductivity type on the semiconductor substrate isperformed (step S2). Specifically, the epitaxial layer is formed on thesilicon carbide substrate by a chemical vapor deposition (CVD) processusing hydrocarbon and silane gas. In addition, a silicon carbidesubstrate on which the epitaxial layer has already been formed may bebought and used in the following steps.

At this time, to suppress the expansion of the lamination defectoccurring in the case where the current flows in the forward directionof the pn junction (forward conduction), a process of converting thebasal plane dislocation into the other dislocation to reduce the densitythereof, for example, is preferably performed.

Next, an epitaxial layer inspection step of inspecting initialcharacteristics of the epitaxial layer that has been formed is performed(step S3). Specifically, the epitaxial layer has an impurity density, athickness, and a surface state evaluated by a nondestructive techniqueusing a commercial inspection device. Moreover, the crystal defectincluding the basal plane dislocation of each wafer is observed. Thebasal plane dislocation is a linear defect that extends in an off-angledirection correspondingly to a length of the layer thickness of theepitaxial layer grown on the off-angle substrate. The observations areperformed by, for example, a scanning photoluminescence technique or anX-ray topographic observation.

The inspection results are stored as inspection result data in apredetermined memory region (not shown). In addition, the inspectionsare performed in a wafer state.

Here, the crystal defect including the basal plane dislocation causesthe expansion of the lamination defect. The expansion of the laminationdefect causes an increase in a forward resistance of the semiconductordevice, so that the semiconductor wafer having the low density of thecrystal defects is preferably manufactured.

Moreover, the crystal defects including the basal plane dislocation aredistributed in a concentrated manner and may be similarly distributed inthe epitaxial layers of the plurality of silicon carbide semiconductorsubstrates of the same boule or the same lot. Such case eliminates theneed to observe the crystal defects in the epitaxial layers of all thesilicon carbide semiconductor substrates, and the observations may bereplaced with observations of the crystal defects in part of the siliconcarbide semiconductor substrates that are selected on the boule basis orthe manufacturing lot basis. In this manner, the cost and the time forthe inspections can be reduced, resulting in the reduced manufacturingcosts.

Next, a wafer processing step of manufacturing a semiconductor elementis performed (step S4). Specifically, a commercial semiconductormanufacturing device is used to repeat pattern expose and development,and furthermore, an etching, an ion (impurity) implantation, heattreatment, oxidation treatment, formation of an interlayer film, andformation of an electrode are performed, to thereby manufacture thesilicon carbide semiconductor MOSFET on the semiconductor wafer.

Next, a wafer test step of evaluating the initial characteristics of thesemiconductor wafer is performed (step S5). Specifically, the initialcharacteristics of the element are evaluated using a normal prober orthe like. A leakage current in the semiconductor wafer is also measured.The test results are stored as the inspection result data in thepredetermined memory region (not shown).

Next, a dicing step of dicing the semiconductor wafer to formsemiconductor chips is performed (step S6). A normal dicer is used forthe dicing.

Next, a chip test step of evaluating the initial characteristics of thesemiconductor chip (semiconductor element) is performed (step S7). Thetest results are stored as the inspection result data in thepredetermined memory region (not shown). The leakage current in thesemiconductor chip is also measured. Moreover, a resistance value andthe amount of change in resistance relative to conduction time are alsomeasured in a case where a current of approximately 10 A/cm² flows, forexample.

Next, the presence or absence of the increase in the forward resistancein a case of the forward conduction in the pn junction in thesemiconductor chip is determined with reference to at least one of theinspection result data obtained in the previous steps. Then, if noforward resistance is determined to be increased, the semiconductor chipis assumed as a semiconductor chip of a first group suitable for theforward conduction. If the forward resistance is determined to beincreased, the semiconductor chip is assumed as a semiconductor chip ofa second group unsuitable for the forward conduction.

For example, with reference to the inspection result data of theepitaxial layer inspection step (step S3), the silicon carbidesemiconductor substrate having the crystal defect in the epitaxial layermay be assumed as a semiconductor wafer unsuitable for the forwardconduction.

Moreover, for example, with reference to the inspection result data ofthe wafer test step (step S5), the semiconductor wafer having abnormalrectifying characteristics of a body diode as an element structure andhaving the leakage current relatively greater than the normaldistribution may be assumed as a semiconductor wafer unsuitable for theforward conduction.

Moreover, for example, with reference to the inspection result data ofthe chip test step (step S7), the semiconductor chip having the leakagecurrent greater than the predetermined threshold value or having theamount of change in the forward resistance in the conductive stategreater than the predetermined threshold value may be assumed as asemiconductor wafer unsuitable for the forward conduction.

Then, a classification step of classifying an use of the semiconductorchip according to each group is performed (step S8). By thisclassification, the semiconductor chip of the first group suitable forthe forward conduction (Yes) continues to a step of installing thesemiconductor chip in the silicon carbide semiconductor device havingspecifications that need the forward conduction in the pn junction inthe semiconductor chip, and the semiconductor chip of the second groupunsuitable for the forward conduction (No) continues to a step ofinstalling the semiconductor chip in the silicon carbide semiconductordevice having specifications that do not need the forward conduction inthe pn junction in the semiconductor chip.

Next, an assembly step of fixing each of the semiconductor chip of thefirst group and the semiconductor chip of the second group to a case ora mold to form wiring is performed (step S9-1 and step S9-2). Inaddition, the step is performed in a chip state.

Next, a product inspection step of inspecting initial characteristics ofeach silicon carbide semiconductor device (product) that has beenassembled is performed (step S10-1 and step S10-2). In this manner, thesilicon carbide semiconductor device (product) is manufactured.

FIGS. 2 and 3 are circuit diagrams of silicon carbide semiconductorMOSFETs as an example of a silicon carbide semiconductor device that ismanufactured.

FIG. 2 is the circuit diagram of a silicon carbide semiconductor MOSFET10 including the semiconductor chip of the first group.

The silicon carbide semiconductor MOSFET 10 shown in FIG. 2 is disposedon a chip package 20. A body diode 1 in the silicon carbidesemiconductor MOSFET 10 is suitable for the forward conduction, so thatthe silicon carbide semiconductor MOSFET 10 is manufactured as a siliconcarbide semiconductor device having specifications that need the forwardconduction in the pn junction.

Meanwhile, FIG. 3 is the circuit diagram of a silicon carbidesemiconductor MOSFET 10A including the semiconductor chip of the secondgroup.

The silicon carbide semiconductor MOSFET 10A shown in FIG. 3 is disposedon a chip package 20. A body diode 1A in the silicon carbidesemiconductor MOSFET 10A is not suitable for the forward conduction, sothat the chip package 20 further includes an SiC Schottky diode 2thereon, the SiC Schottky diode 2 being connected in parallel to thebody diode 1A of the silicon carbide semiconductor MOSFET 10A. The SiCSchottky diode 2 is arranged such that the forward direction thereof isin the same direction as the forward direction of the body diode 1A. Inaddition, an Si diode may be provided instead of the SiC Schottky diode2.

The SiC Schottky diode 2 functions as a feedback diode (free-wheeldiode) of the silicon carbide semiconductor MOSFET 10A. Thus, theincrease in the forward resistance of the body diode 1A of the siliconcarbide semiconductor MOSFET 10A does not contribute to the forwardcharacteristics of the silicon carbide semiconductor MOSFET 10A.

<Modifications>

To simplify the manufacturing steps, any of the inspection steps (stepsS3, 5, and 7) in FIG. 1 may only be performed. It should be noted thatthe classification step (step S8) can perform the classification withhigher accuracy in a case of referring to more inspection result data.

The classification step (step S8) may be performed, for example, afterthe epitaxial layer inspection step (step S3) and before the waferprocessing step (step S4) or may be performed after the wafer test step(step S5) and before the dicing step (step S6).

In this manner, the classification performed in the earlier step allowsfor a higher degree of flexibility in structural modifications.

If the classification is performed before the wafer processing step(step S4), the wafer processing step (step S4) can perform exposuretreatment in which different exposure masks can be used for the firstgroup and the second group, allowing for the formation of identificationdisplay so as to enable the distinction between the first group and thesecond group in a case of being divided by the dicing.

Moreover, if the classification is performed before the dicing step(step S6), the dicing step (step S6) can dice along the boundary betweenthe first group and the second group. Thus, the first group and thesecond group can be suppressed to mix together in one semiconductorchip. Consequently, the silicon carbide semiconductor device can bemanufactured using the least wasted semiconductor chip.

<Effects>

In this embodiment of the present invention, the method formanufacturing the silicon carbide semiconductor device includes thesteps of: (a) inspecting the characteristics of the forward conductionof the body diode 1 and the body diode 1A as the element structures; (b)classifying the body diode 1 and the body diode 1A as the first groupsuitable for the forward conduction or the second group unsuitable forthe forward conduction on the basis of the inspection result of the step(a); and (c) manufacturing the silicon carbide semiconductor device 10that needs the forward conduction in the body diode 1 using the bodydiode 1 of the first group or manufacturing the silicon carbidesemiconductor device 10A that does not need the forward conduction inthe body diode 1A using the body diode 1A of the second group.

This configuration classifies the body diode 1 and the body diode 1A asthe body diode 1 of the first group or the body diode 1A of the secondgroup and manufactures the silicon carbide semiconductor MOSFET 10 andthe silicon carbide semiconductor MOSFET 10A according to each use.Thus, the element structure unsuitable for the forward conduction is notregarded as a defective product and is effectively used to manufacturethe silicon carbide semiconductor device, so that the increase in thecost of manufacturing one chip can be prevented while the forwardcharacteristics of the silicon carbide semiconductor device for each useare favorably maintained.

Moreover, the forward characteristics of the element structure areclassified before the silicon carbide semiconductor device ismanufactured, and thus the following steps have a higher degree offlexibility in structural modifications.

In this embodiment according to the present invention, the differentexposure masks are used in the case where the silicon carbidesemiconductor MOSFET 10 including the body diode 1 of the first group ismanufactured and in the case where the silicon carbide semiconductorMOSFET 10A including the body diode 1A of the second group ismanufactured.

This configuration can form the identification display so as to enablethe distinction between the body diode 1 of the first group and the bodydiode 1A of the second group. Thus, the first group and the second groupare appropriately distinguished even in the case of being divided by thedicing in the following steps and can be prevented from being mixedtogether.

Furthermore, the embodiment according to the present invention furtherinstalls the SiC Schottky diode 2 that is connected in parallel to thebody diode 1A and has the same forward direction as the forwarddirection of the body diode 1A in the case where the silicon carbidesemiconductor MOSFET 10A using the body diode 1A of the second group ismanufactured.

The SiC Schottky diode 2 functions as the feedback diode (free-wheeldiode) of the silicon carbide semiconductor MOSFET 10A. Thus, theincrease in the forward resistance of the body diode 1A of the siliconcarbide semiconductor MOSFET 10A does not contribute to the forwardcharacteristics of the silicon carbide semiconductor MOSFET 10A.

Furthermore, the embodiment according to the present invention includesthe step of observing the crystal defect in the epitaxial layer by thescanning photoluminescence technique to inspect the characteristics ofthe forward conduction in the body diode 1 and the body diode 1A.

This configuration allows for the observation by the nondestructivetechnique that is different from the observation using a transmissiontype electron microscope or the like. This eliminates the need toprepare the semiconductor substrate for inspection. In addition, thedevice is relatively low-priced, and the inspection cost can besuppressed.

Additionally, the time and cost can be suppressed compared to the casewhere a screening is performed by the conduction to inspect the forwardcharacteristics. Furthermore, this method can accurately inspect thecrystal defect having a shape, size, or the like in which no noticeabledifference appears by the conduction.

Furthermore, the embodiment according to the present invention includesthe step of observing the crystal defect in the epitaxial layer by theX-ray topographic observation technique to inspect the characteristicsof the forward conduction in the body diode 1 and the body diode 1A.

This configuration allows for the observation of detailed dislocationand the classification with higher accuracy.

Additionally, the time and cost can be suppressed compared to the casewhere the screening is performed by the conduction to inspect theforward characteristics. Furthermore, this method can accurately inspectthe crystal defect having the shape, size, or the like in which nonoticeable difference appears by the conduction.

Furthermore, the embodiment according to the present invention observesthe crystal defect in the epitaxial layer on part of the silicon carbidesemiconductor substrate that is selected on the boule basis or themanufacturing lot basis to inspect the characteristics of the forwardconduction in the body diodes.

This configuration can efficiently perform the inspection and reduce theinspection cost and the inspection time.

Second Embodiment Manufacturing Method

FIG. 4 is a flow chart illustrating an outline of a method formanufacturing a silicon carbide semiconductor device according to thisembodiment. FIG. 4 shows the same steps S1 to 7 as those of the firstembodiment, so that detailed description will be omitted.

After the step S7, an assembly step of fixing a semiconductor chip to acase or a mold to form wiring is performed (step S9).

Next, a product inspection step of inspecting initial characteristics ofthe silicon carbide semiconductor device (product) that has beenassembled is performed (step S10). The inspection result is stored asinspection result data in a predetermined memory region.

Next, a screening step of inspecting the presence or absence ofdeterioration in a case of the forward conduction in a pn junction inthe silicon carbide semiconductor device (product) is performed (stepS11). Specifically, the presence or absence of an increase in theforward resistance is inspected by an initial conduction in which a bodydiode of the silicon carbide semiconductor device is energized in theforward direction. The inspection result is stored as the inspectionresult data in the predetermined memory region.

Next, with reference to at least one of the inspection result dateobtained in the previous steps, a classification step of classifying anuse according to each of the silicon carbide semiconductor device havingan element structure of a first group suitable for the forwardconduction and the silicon carbide semiconductor device having anelement structure of a second group unsuitable for the forwardconduction is performed (step S8). In this manner, the silicon carbidesemiconductor device (product) classified according to each use ismanufactured.

FIGS. 2 and 5 are the circuit diagrams of the silicon carbidesemiconductor MOSFETs as an example of silicon carbide semiconductordevices that are each used or manufactured in the next step, which isnot shown in FIG. 4, in cases of Yes and No in the step S8.

FIG. 2 is the circuit diagram of the silicon carbide semiconductorMOSFET 10 including the semiconductor chip of the first group in thecase of Yes in the step S8.

The silicon carbide semiconductor MOSFET 10 shown in FIG. 2 is disposedon the chip package 20. The body diode 1 in the silicon carbidesemiconductor MOSFET 10 is suitable for the forward conduction, so thatthe silicon carbide semiconductor MOSFET 10 is manufactured as a siliconcarbide semiconductor device having specifications that need the forwardconduction in the pn junction.

Meanwhile, FIG. 5 is the circuit diagram of a silicon carbidesemiconductor MOSFET 10A including the semiconductor chip of the secondgroup in the case of No in the step S8.

The silicon carbide semiconductor MOSFET 10A shown in FIG. 5 is disposedon a chip package 20. A body diode 1A in the silicon carbidesemiconductor MOSFET 10A is unsuitable for the forward conduction, sothat a chip package 21 different from the chip package 20 furtherincludes a SiC Schottky diode 3 thereon, the SiC Schottky diode 3 beingconnected in parallel to the body diode 1A of the silicon carbidesemiconductor MOSFET 10A. The SiC Schottky diode 3 is arranged such thatthe forward direction thereof is in the same direction as the forwarddirection of the body diode 1A. In addition, an Si diode may be providedinstead of the SiC Schottky diode 3.

The SiC Schottky diode 3 functions as a feedback diode (free-wheeldiode) of the silicon carbide semiconductor MOSFET 10A. Thus, theincrease in the forward resistance of the body diode 1A of the siliconcarbide semiconductor MOSFET 10A does not contribute to the forwardcharacteristics of the silicon carbide semiconductor MOSFET 10A.

<Modifications>

To simplify the manufacturing steps, any of the inspection steps (stepsS3, 5, 7, 10, and 11) in FIG. 4 may only be performed. It should benoted that the classification step (step S8) can perform theclassification with higher accuracy in a case of referring to moreinspection result data.

The classification step (step S8) may be performed after the productinspection step (step S10) and before the screening step (step S11). Theclassification performed in the earlier step allows for a higher degreeof flexibility in structural modifications.

<Effects>

This embodiment of the present invention includes the steps of: (a)inspecting the characteristics of the forward conduction of the bodydiode 1 and the body diode 1A as the element structures; (b)manufacturing the silicon carbide semiconductor device 10 and thesilicon carbide semiconductor device 10A using the body diode 1 and thebody diode 1A, respectively; and (c) classifying the silicon carbidesemiconductor device 10 and the silicon carbide semiconductor device 10Athat have been manufactured as the silicon carbide semiconductor device10 having the body diode 1 of the first group suitable for the forwardconduction or the silicon carbide semiconductor device 10A having thebody diode 1A of the second group unsuitable for the forward conductionon the basis of the inspection result of the step (a).

This configuration can increase the inspection result data that can bereferred to and perform the classification with higher accuracy.

Each embodiment described above shows the example of the MOSFET thatneeds the body diode to be energized, for example, as the siliconcarbide semiconductor device that needs the forward conduction in the pnjunction. Similarly, in a method for manufacturing a silicon carbidesemiconductor device of a type in which a pn junction of a thyristor, anIGBT, and a heterobipolar transistor, for example, is energized in theforward direction, the conduction in the pn diode eliminates adeteriorating element structure, achieving effects of improvingreliability of the conduction.

Although the materials of the respective components, the conditions ofimplementation, and the like, are described in the embodiments of thepresent invention, the forgoing description is illustrative and notrestrictive.

In addition, according to the present invention, the above embodimentscan be arbitrarily combined, or each embodiment can be appropriatelyvaried or omitted within the scope of the invention.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood the numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF NUMERALS

1, 1A body diode; 2, 3 SiC Schottky diode; 10, 10A silicon carbidesemiconductor MOSFET; 20, 21 chip package.

The invention claimed is:
 1. A method for manufacturing a siliconcarbide semiconductor device that has an element structure including anepitaxial layer of a first conductivity type formed on a silicon carbidesemiconductor substrate of a first conductivity type and an impuritylayer of a second conductivity type formed in contact with saidepitaxial layer, said method comprising the steps of: (a) inspectingcharacteristics of a forward conduction between said epitaxial layer andsaid impurity layer in said element structure; (b) classifying saidelement structure as a first group suitable for said forward conductionor a second group unsuitable for said forward conduction on the basis ofan inspection result of said step (a); and (c) manufacturing a MOSFETdevice using said element structure of said first group andmanufacturing a MOSFET device coupled to a Schottky diode using saidelement structure of said second group.
 2. The method for manufacturinga silicon carbide semiconductor device according to claim 1, whereinsaid step (c) is a step of using different exposure masks in the casewhere said silicon carbide semiconductor device is manufactured usingsaid element structure of said first group and in the case where saidsilicon carbide semiconductor device is manufactured using said elementstructure of said second group.
 3. A method for manufacturing a siliconcarbide semiconductor device that has an element structure including anepitaxial layer of a first conductivity type formed on a silicon carbidesemiconductor substrate of a first conductivity type and an impuritylayer of a second conductivity type formed in contact with saidepitaxial layer, said method comprising the steps of: (a) inspectingcharacteristics of a forward conduction between said epitaxial layer andsaid impurity layer in said element structure; (b) classifying saidelement structure as a first group suitable for said forward conductionor a second group unsuitable for said forward conduction on the basis ofan inspection result of said step (a); and (c) manufacturing saidsilicon carbide semiconductor device that needs said forward conductionin said element structure using said element structure of said firstgroup and manufacturing said silicon carbide semiconductor device thatdoes not need said forward conduction in said element structure usingsaid element structure of said second group, wherein said step (c) is astep of further installing a diode that is connected in parallel to saidelement structure and has the same forward direction as the forwarddirection of said element structure in the case where said siliconcarbide semiconductor device is manufactured using said elementstructure of said second group.
 4. The method for manufacturing asilicon carbide semiconductor device according to claim 1, wherein saidstep (a) is a step of inspecting the characteristics of said forwardconduction in said element structure by performing at least one ofobservation of a crystal defect in said epitaxial layer, measurement ofa leakage current in said element structure, and measurement of timechange in a forward resistance in a case where said element structure isenergized in a forward direction.
 5. The method for manufacturing asilicon carbide semiconductor device according to claim 4, wherein saidstep (a) includes a step of observing the crystal defect in saidepitaxial layer by a scanning photoluminescence technique to inspect thecharacteristics of said forward conduction in said element structure. 6.The method for manufacturing a silicon carbide semiconductor deviceaccording to claim 4, wherein said step (a) includes a step of observingthe crystal defect in said epitaxial layer by an X-ray topographicobservation technique to inspect the characteristics of said forwardconduction in said element structure.
 7. The method for manufacturing asilicon carbide semiconductor device ac cording to claim 4, wherein saidstep (a) includes a step of observing the crystal defect in saidepitaxial layer on part of said silicon carbide semiconductor substratethat is selected on a boule basis or a manufacturing lot basis toinspect the characteristics of said forward conduction in said elementstructure.